Voltammetry as a Reference Method in the Preparation Process of Plant Control Material Containing As,Pt and Tl

Voltammetric methods are very suitable and versatile techniques for the simultaneous metal determination in complex matrices after thorough mineralization. In the presented work, voltammetric methods were used as reference methods in the preparation process of control plant material. Determination of As, Pt, Tl and other elements (Cd, Cu, Pb, Zn) in plant material prepared in our laboratory is described. For quantitative determination of the elements two independent analytical methods were applied. To obtain plant material containing As, Pt and Tl white mustard (Sinapis alba L.) was hydroponically cultivated under controlled conditions in a nutrient solution with addition of As, Pt and Tl salts.     

Crystal structure of lead(II) acetylacetonate and the structure of the acetylacetone solvated lead(II) ion in solution studied by large-angle X-ray scattering

The crystal structure of bis(acetylacetonato)lead(II) and the structure of the acetylacetone solvated lead(II) ion in solution have been determined by single-crystal X-ray diffraction and large-angle X-ray scattering (LAXS), respectively. The acetylacetone is deprotonated and acts as a bidentate anionic ligand (acac-) in the solid Pb(acac)2 compound. The lead(II) ion binds four oxygen atoms strongly in a nearly flat pyramidal configuration with Pb-O bond lengths in the range 2.32-2.37 A, and additionally three oxygens from neighboring complexes at 3.01-3.26 A. Acetylacetone acts as a solvent (Hacac) at dissolution of lead(II) trifluoromethanesulfonate forming a pentasolvate with a mean Pb-O bond distance of 2.724(5) A. The 6s2 lone electron pair on the lead(II) ion becomes stereochemically active in the crystalline acetylacetonate complex, while it is inactive in the solvate in solution. The solution was also analysed using IR and 1H NMR spectroscopy.     

Stoichiometry determination of (Pb,La)(Zr,Ti)O3-type nano-crystalline ferroelectric ceramics by wavelength-dispersive X-ray fluorescence spectrometry

Analysis of small samples of lanthanum-doped lead zirconate titanate (PLZT) by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) is presented. The powdered material in ca. 30 mg was suspended in water and collected on the membrane filter. The pure oxide standards (PbO, La₂O₃, ZrO₂ and TiO₂) were used for calibration. The matrix effects were corrected using a theoretical influence coefficients algorithm for intermediate-thickness specimens. The results from XRF method were compared with the results from the inductively coupled plasma optical emission spectrometry (ICP-OES). Agreement between XRF and ICP-OES analysis was satisfactory and indicates the usefulness of XRF method for stoichiometry determination of PLZT.     

Efficient synthesis of meso-substituted corroles in a H2O-MeOH mixture

New and efficient conditions for the synthesis of meso-substituted corroles were developed. The first step, involving the reaction of aldehydes with pyrrole, was carried out in a water-methanol mixture in the presence of HCl. A relatively narrow distribution of aldehyde-pyrrole oligocondensates was obtained through careful control of their solubility in the reaction medium. After thorough optimization of various reaction parameters (cosolvent, reagent, and acid concentration), high yields of bilanes were obtained. Additionally, the bilane derived from 4-cyanobenzaldehyde was isolated, and the oxidative macrocyclization reaction was performed under various reaction conditions (different solvents, different concentrations, and various oxidants). As a result, triphenylcorrole was obtained in the highest yield (32%) reported to date. The scope and limitations studied showed that this method was particularly efficient for moderately reactive aldehydes and those bearing electron-donating groups (yields 14-27%). Using these conditions, corroles bearing strongly electron-donating groups were obtained for the first time. In addition, it was found that the reaction of unhindered dipyrromethanes with aldehydes under analogous conditions afforded trans-A2B-corroles in very high yields (45-56%; 8-fold higher than previously reported) without scrambling. The fact that scrambling was not observed in this reaction despite a very high HCl concentration (0.3 M) is unprecedented. Detailed studies on the oxidation of bilane, derived from sterically hindered dipyrromethane, allowed us to unequivocally establish that the yield of macrocyclization is insensitive to the concentration. It was found the 1H NMR spectra of corroles in deuterated TFA gave very sharp signals.     

N-Hydroxyphthalimide in combination with Cu(II), Co(II) or Mn(II) salts as catalytic systems for the oxidation of isopropyl-aromatic hydrocarbons with oxygen

Catalytic systems consisting of N-hydroxyphthalimide in combination with copper(II), cobalt(II) and manganese(II) acetylacetonate, acetate or chloride were applied to the oxidation of cumene with oxygen. The use of these catalytic systems decreases cumyl hydroperoxide selectivity as a result of the decomposition reaction of hydroperoxide to 2-phenyl-2-propanol and acetophenone. It has been demonstrated that the use of N-hydroxyphthalimide in combination with copper salts at 60 °C results in high alcohol content whereas ketone is the major product at 90 °C. The results can be used to develop a method for alcohol or ketone synthesis from other isopropyl-aromatic hydrocarbons.     

Reactions of nitrophenide and halonitrophenide ions with acrylonitrile and alkyl acrylates in the gas phase: addition to the carbonyl group versus Michael addition

Gas-phase reactions of isomeric nitrophenide ions and p-halonitrophenide ions with acrylonitrile, methyl acrylate, and ethyl acrylate have been studied using mass spectrometry and computational methods. Depending on the structure of the α,β-unsaturated compound, formation of adducts to the carbonyl group of the acrylate (for methyl acrylate and ethyl acrylate) and β-adducts (adducts of p-halonitrophenide ions to α,β-unsaturated compounds in β position) was observed. Further transformations of these adducts lead to the products of elimination of an alcohol molecule and the anionic products of intramolecular substitution of a halogen atom, respectively.     

On isometric stability of complemented subspaces of L p

We show that the Rudin-Plotkin isometry extension theorem inL _pimplies that whenX andY are isometric subspaces ofL _pandp is not an even integer, 1≤p<∞, thenX is complemented inL _pif and only ifY is; moreover, the constants of complementation ofX andY are equal. We provide examples demonstrating that this fact fails whenp is an even integer larger than 2.     

Development of Liquid Crystalline Order During Cure of Mesogenic Epoxy Resins

In the present paper we describe the curing process of a new liquid crystalline epoxy monomer with 4,4′-diaminodiphenylenemethane (DDM). The characteristic of cured product is presented. Both the monomer and cured product have been characterized by IR and NMR spectroscopy, differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and dielectric relaxation spectroscopy (DRS).The curing process was analysed with the use of DSC and real-time DRS.